Not published in LIFE. Sinatra and Martin take a cigarette break during the recording of Sleep Warm in 1958. The album was re-released in 1963 with a much more direct title: Dean Martin Sings/Sinatra Conducts.

That, legend has it, is what Frank Sinatra joked upon hearing the plot for Ocean’s 11, the 1960 Vegas heist flick that went on to become the Rat Pack’s signature big-screen adventure.

It’s no wonder Sinatra and his kindred crew of high-living, hard-drinking, skirt-chasing buddies — Dean Martin and Sammy Davis Jr., especially — were gassed to make such a movie: just like their characters, they loved a good caper. From the late ’50s until they began to splinter apart in the mid-’60s, they were showbiz’s unrivaled kings of swing, quick-with-a-quip cats who could swagger into any joint — from the Sands to Sardi’s — and make it the most.

LIFE magazine’s photographers trailed the Pack through those smoky, magical years, coming away with priceless material for some of the best celebrity photo-essays the magazine ever ran. But of the thousands of shots taken, many were never published — until now. Here, in celebration of sharkskin sits, Scotch on the rocks, smoke-filled rooms and fedoras tilted just so, LIFE presents a slew of rare photos of the Rat Pack, together and apart, during their boozy heyday.